The recent proliferation of computer-controlled devices for performing a wide variety of tasks can be at least partially attributed to the development of powerful and convenient communications interface standards, such as various types of serial bus interfaces. Some of them have conveniently incorporated remote electrical powering to the communication functionality of the interface, so that peripheral devices that do not require excessive electrical power to operate could be powered remotely through the communications interface rather than requiring a built-in or a separate power supply at the device location. One such interface standard that has now become ubiquitous is the Universal Serial Bus (USB).
The USB is a peripheral hub-centric serial bus that is widely used to facilitate coupling of a wide range of simultaneously accessible peripheral devices to a host computer system. The bus allows up to 127 peripheral devices to be attached, configured, used, and detached while the host is in operation. For example, USB printers, scanners, digital cameras, storage devices, card readers, etc. may communicate with a host computer system over USB. USB based systems may require that a USB host controller be present in the host system, and that the operating system (OS) of the host system support USB and USB Mass Storage Class Devices. As compared to other ways of connecting devices to the computer, such as parallel ports, serial ports and custom cards installed inside the computer's case, the USB devices are relatively simple. If the USB device is a new device, the OS auto-detects the USB device and may initiate a dialog with the user to locate a driver for the USB device. If the USB device has already been installed, the computer activates the USB device.
USB devices may communicate with the USB host at low-speed (LS), full-speed (FS), or high-speed (HS). USB Specification version 1.1 supports two different rates for transmitting data: A Low Speed (LS) rate of 1.5 Mega bits (Mbits) per second that is mostly used for low-speed human interface type devices such as keyboards and mice, and a Full-Speed (FS) rate of 12 Mbits/second for most other devices. USB Specification 2.0 adds a High-Speed (HS) rate of 480 Mbps for communications with high speed devices. The USB Specification Revision 2.0, Apr. 27, 2000, which describes the USB 2.0 protocol in detail, is available on-line at http://www.usb.org/developers/docs and is incorporated herein by reference in its entirety.
A connection between the USB device and the USB host is typically established via a four wire interface that is formed by 4-pin USB connectors and a USB cable that includes four wires: two wires for providing a 5V dc power signal and ground, respectively, and a twisted pair of wires to carry data, which are labeled as D+ and D−, and are used for half-duplex differential signaling to combat the effects of electromagnetic noise on longer lines, with the data sent in digital format using a NRZI (Non Return to Zero Invert) encoding scheme.
Advantageously, low-power devices such as mice, video cameras, and/or other devices can draw their power directly from the USB connection. High-power devices such as printers and/or other devices have power supplies and typically draw minimal power from the USB connection. USB devices are hot-swappable, which means that they can be plugged and unplugged at any time. Up to 127 devices can be connected to any one USB bus at any one given time. At system turn-on, the host computer powers up, queries all of the USB devices connected to the bus and assigns an address to each USB device. This process is called enumeration; USB devices are also enumerated when they are connected to the bus in operation. The host computer determines the type of data transfer that the USB device employs, such as an interrupt mode, a bulk transfer mode, or an isochronous mode.
Due to it numerous advantages and ease of operation, the USB protocol is now the prevalent protocol for communication between computers and peripheral devices of different kind. Various sensors, transducers as well as more recently GPS devices and video cameras are now available with a USB interface that provides both power and the entire data transmission between the device and a computer in a digital format. This universality leads to acceptance of the USB protocol as a standard protocol for peripheral communications, as well as the proliferation of digital data transmission for a variety of applications.
However, the traditional USB links involving communications over 4-wire USB cables cannot be longer than 5 meters, therefore limiting possible applications to a desktop type environment. This is in part due to strict limitations that the current USB specification imposes on the cable delay time, which should not exceed 26 ns for a single cable. There is however another important limitation on the maximum length of a traditional USB cable, namely—signal attenuation, which in traditional 4-wire USB cables strongly increases with signal frequency, typically from about 0.7 dB/m at 10 MHz to as high as 5.8 dB/m at 400 MHz. This signal attenuation makes it difficult to impossible to use cables in excess of 5-10 meters at full and, especially, high data transfer speed.
Another limitation of the traditional USB copper-based links is their potential susceptibility to high magnetic, voltage and RF fields, which may induce errors in USB data transmission. Furthermore, the traditional copper-based USB cables can themselves be a source of electromagnetic interference (EMI), and therefore their use can cause undesirable problems in EMI-sensitive environments.
U.S. Pat. No. 6,950,610 issued to Lee and assigned to Opticis Co., LTD, which is incorporated herein by reference, has disclosed an optical communication interface module for connecting USB interfaces through an optical fiber line that employs separate optical fibers to transmit optical signals in each direction. However, the optical communication interface module of Lee only partially solves the above stated problems, since operating a USB device using it will either still require two separate copper lines VCC and GND to remotely power the device, or require an external power supply at the device location, which may be inconvenient or even close to impossible in some applications. The optical communication interface modules of Lee therefore do not provide a fully-functional all-optical alternative to a USB cable, which would be beneficial in applications where conventional copper USB cables cannot be used, such as in EMI sensitive environments.
It is therefore desirable to provide a USB link and USB interface modules that can be used in EMI sensitive environments or in the presence of high magnetic, electrical and RF fields to remotely operate and to power conventional USB devices.
An object of the present invention is to overcome the shortcomings of the prior art by providing an optically powered optical data link and optical interface modules for remotely powering and operating peripheral devices using a desired communications protocol, and to provide an optically powered optical data link and optical interface modules that are capable of operating in EMI sensitive environment or in the presence of strong electrical, magnetic or RF fields.